The state-of-the-art method for electrolyzing an alkali metal halide, especially sodium chloride (NaCl) or potassium chloride (KCl), is to use a fluorinated membrane to separate the anolyte and catholyte compartments of an electrolytic cell. The membrane permits the alkali metal cation to pass through to the catholyte, but severely restricts the undesirable passage of hydroxyl ion from the catholyte to the anolyte. State-of-the-art fuel cells also use fluorinated membranes to separate the anolyte and catholyte compartments of the cell. Fluorinated membranes are also useful in conventional chemical separations and facilitated transport processes. To make these membranes more attractive, water absorption and ionic conductivity of the membrane should be increased.
Many efforts have been made to improve the performance of these membranes, particularly membranes used in chloralkali cells or fuel cells, by a wide variety of treatments. Most of the efforts have been aimed at obtaining lower voltage, higher current efficiency or lower power consumption.
Water absorption is also an important factor. Increased water content of the ionomeric material usually increases the ion conductivity of the polymer membrane.
It is known that the irradiation of a fluorinated ion exchange membrane may improve cell voltage. U.S. Pat. No. 5,128,014 (Banerjee) discloses and claims a process for irradiating a fluorinated ion exchange membrane.
U.S. Pat. No. 4,439,292 (Klotz et al.) also teaches irradiation of perfluorinated polymeric membranes in the presence of a monomer in order to facilitate cross-linking of the membrane to lower voltage in an electrolytic cell. U.S. Pat. No. 4,439,292 reduced cell voltage by treating fluorinated carboxyl membranes with corona discharge, a process in which an electrical discharge or spark is passed from one electrode to another through a gas and through the sample to be treated. Klotz et al. found that heating damaged the membrane. They chose to keep the temperature below 80.degree. C., preferably below +22.degree. C., and most preferably below -20.degree. C. To prevent heat damage, Klotz et al. exposed the sample to corona discharge 1000-5000 times, with cooling between exposures. Clearly, the need to use thousands of exposures is a severe limitation to the usefulness of this process.